The present invention relates to a method of refining iron ore in which the iron ore is reduced to iron containing products. More particularly, the present invention relates to such a method in which char formed from a carbon containing substance, such as coal, is gasified in the reduction of the iron ore. Even more particularly, the present invention relates to such a method in which the char is formed and all or part of the iron ore to be refined is partly reduced within a secondary reactor and the resultant char and partly reduced iron ore are fed into a higher temperature primary reactor for production of the iron containing products.
There are various iron refining processes that include the use of electric arc, open hearth, blast furnaces, the COREX.RTM. Process, and primary bath smelting reactors such as are used in the ROMELT process. In all of such reactors, a charge of iron ore and a carbon containing substance such as coal or coke is introduced into a reactor. Oxygen or oxygen enriched air is also introduced into the reactor to gasify the carbon containing material to produce a reducing gas containing hydrogen and carbon monoxide. The reducing gas acts to reduce the ore, thereby to produce an iron containing substance such as a mixture of steel or iron and a separate slag phase.
In the COREX.RTM. process, iron ore and flux are introduced into a shaft furnace to reduce the iron to the solid metal and calcine the flux with a reducing gas produced in the melter-gasifier. Coal or coal that is preheated by combustion of the coal volatiles, known as hot char, is introduced into a melter gasifier along with the directly reduced iron and flux from the shaft furnace and oxygen. The char is gasified and the ore from the shaft furnace is further reduced and melted to produce a molten mixture of iron and slag that can be withdrawn as a product stream. In a primary bath smelting reactor, such as used in the ROMELT process, oxygen, iron ore and coal are introduced into a reactor to produce iron and slag products.
In any of the above-mentioned processes it is desired to maximize the productivity of the reactor. Further, all of the above-mentioned processes use processed oxygen, namely oxygen having a purity of about 95% or greater or oxygen enriched air. Such processed oxygen contributes to the cost of production. Thus, a reduction in required processed oxygen usage allows either reduced production costs or more productivity with no increase in cost, at least with respect to oxygen usage. As will be discussed, the present invention provides a method that can be used in connection with any of the above-mentioned processes that allows for an increase in reactor productivity accompanied by a reduction in the usage of processed oxygen.